Nowak enjoyed a successful playing career in Europe, playing for Polish clubs such as Zawisza Bydgoszcz and Widzew Łódź, before going on to play in Turkey, Switzerland and Germany. He was voted one of the best players in the Bundesliga for the 1995–96 season while playing with 1860 Munich. He moved to the United States in 1998 and played four years with Chicago Fire.

Nowak was also an important member of the Poland national football team throughout the 1990s, earning 24 caps, serving as national captain for several years, and being voted Polish Player of the Year in 1996.

Piotr Nowak ’s storied soccer journey began in Pabianice, a small town in Poland. He signed his first professional contract at the age of 15 to pursue his soccer dreams. He played in Polish First Division for Zawisza Bydgoszcz and Widzew Lodz.

In 1998, Nowak moved to the United States and joined the Chicago Fire for the team ’s inaugural MLS season. He promptly established himself as one of the best players in the League, leading the Fire to a MLS Cup (1998) and two US Open Cups (1998, 2000). He was elected 3 times to MLS All Star Team, 3 times as Chicago Fire MVP and 3 times as MLS Best XI including 1998 MLS Cup MVP. Nowak patrolled the Fire midfield for 114 league games, registering 26 goals and 48 assists. He played with Chicago for five seasons and retired in 2003. He was inducted as a first member of “Ring of Fire” Chicago Fire’s Hall of Fame in 2004.

Wilst still playing for clubs in the United States, he became chairman of Górnik Konin in 1999. Manager Jerzy Kasalik was sacked for unexplained reasons[9][10] by Nowak, despite their first place in the league, and he appointed little-known manager Jarosław Kotas. The team soon started to lose matches at an alarming rate and only just managed to escape relegation, only thanks to their good start.[11][12]

The 1999/2000 season proved to be a disaster.[13] The owners decided to rename the senior team KP Konin, whilst the reserve and junior teams used the old Aluminium Konin name. The club finished dead last. It then turned out that in the second half of the season plans to relocate the team to Bydgoszcz were put in place, and played under the name Zawisza SSA. In the end the relocation never came to fruition, but the team, which only amassed 8 points the entire season, was disbanded, with the club management and the chairman Piotr Nowak, who played professional football in the USA on a daily basis at the time, widely held responsible.[14][15] The reserve team, which that same season was relegated from the Third Division, became the first team, and a season later (2000/2001 season) managed to gain promotion, going straight back up.

Under the lead of Jerzy Kasalik, the team achieved a back-to-back promotion to the Second Division, restoring the club's place after the first team was disbanded. The success however was short-lived, after in the 2003/04 season the club finished last once again. Following their relegation, many of the Aluminium players were involved in the large corruption scandal in Polish football which shook the country that season, which had a major impact on the club sponsors who all withdrew. This meant that the new club couldn't even afford to play in the then regional Third Division, and the senior team was disbanded.[16][17]

Nowak worked in the Fire front office for one season as a Director of International Relations and Ambassador, before moving to coaching in 2004 when he was hired as head coach of D.C. United. In his first season there, he guided D.C. United to a MLS Cup Championship, with a 3-2 victory over the Kansas City Wizards. With the victory, Nowak became the first man in Major League Soccer history to win a MLS Cup as both a player and a head coach. Additionally, he became the first Head Coach in all major American sports in the last half-century to win a championship within two years of retiring as a player.

In 2005, as part of its 10th anniversary celebration, Major League Soccer named Nowak to its All-Time Best XI, a selection of the best 11 players in the history of MLS. In three years with United, Nowak led the club to win the Supporters ’ Shield and was elected twice as a Head Coach of MLS All Star team (2004, 2006)

That international experience helped as he moved on to become an Assistant to United States Men’s National Team Head Coach Bob Bradley. Nowak also served as Head Coach of the U-23 National Team, advancing to 2008 Olympic Games in Beijing.

Together with Bradley, they coached over 70 players and orchestrated the USA ’s championship run to a title in the 2007 CONCACAF Gold Cup and Mandela Cup. During his time with US Soccer, US Men’s National Team advance from position 31 to 12 in FIFA World Ranking.

On 28 May 2009, Nowak resigned from his position with the United States Men's National Team.[2] Subsequently, the Philadelphia Inquirer reported that Nowak would be the first head coach of the MLS' Philadelphia Union when it begins play in 2010.[3] On Friday, 29 May 2009, Nowak was introduced to the Philadelphia media.

In December 2011 Nowak was named Executive Vice President / Team Manager for the Philadelphia Union. In his only 2nd season as head Coach, the Union made the playoffs for the first and last time in the team’s existence. As a result, Nowak was elected to be the MLS All Star Head Coach for 2012.

Despite all player moves being initiated and approved by Philadelphia Union Board of Directors and CEO/ Operating Partner Nick Sakiewicz, Piotr Nowak was fired by the Union on 13 June 2012 with the Union citing bad trades and a lackluster season. Cost-cutting and financial concerns were at the root of these controversial moves made by the organization including the trade of the Union's leading goal scorer, Sebastian Le Toux, captain Danny Califf, and number one draft pick Danny Mwanga. Nowak began a wrongful termination lawsuit, which was rejected in 2015.[18]

Later, accusations of Nowak mistreating his players surfaced, among the accusations were; repeatedly insulting players, trivialising injuries, making players run in the heat and refusing them water and brutal hazing of rookies.[19][20][21][22][23]

In February 2014, he was hired as a Technical and Personal Advisor to the President of the Caribbean Football Union, which contains 31 countries as a part of CONCACAF. In September 2014, his duties were further grown to include positions as Technical Director and Head Coach of Antigua and Barbuda Football Association, overseeing all National Team Programs including FIFA Grass Roots and Female Programs. Under his direction, Antigua and Barbuda have jumped to 70th place in FIFA World Ranking for the first time in history and is smallest country per capita to be under 100 in FIFA World Ranking.

In 2003, Nowak was named the first member of the Ring of Fire, the highest honor the Chicago Fire bestows, and his name and number 10 are displayed high at midfield at their stadium, Toyota Park. In 2005, Nowak was named to the MLS All-Time Best XI. In 2012, Nowak was honored at a halftime celebration of the Fire's 15th season with other Fire greats.